Recently, liquid crystal display devices have rapidly spread in substitution for cathode-ray tubes (CRT) and have been widely used for liquid crystal televisions, monitors, mobile phones etc. by taking advantages of characteristics of the liquid crystal display devices, such as low energy consumption, flat size, light weight etc. One option for further taking advantage of such characteristics is improvement of an illuminating device (so-called backlight) provided behind a liquid crystal display device.
Illuminating devices are broadly classified into a side light type (also referred to as edge light type) and a direct light type. Among them, the direct light type illuminating device has a plurality of light sources such as cold-cathode tubes behind a liquid crystal display panel and directly illuminates the liquid crystal display panel. Accordingly, the direct light type illuminating device allows obtaining high luminance even for a large screen, and therefore is used mainly for a large liquid crystal display having a 20 inch or more size.
One example of the direct light type illuminating devices is disclosed in Patent Literature 1. In the illuminating unit in Patent Literature 1, a straight-tube light source (linear light source) having electrodes at its both ends is used as a light source. A backlight using such a linear light source is designed such that both ends of the outer shape of the linear light source are positioned at the outside of a region where images are displayed in a liquid crystal display panel (which region is referred to as effective display region) (see FIG. 3 of Patent Literature 1 for example).
This configuration is explained below with reference to drawings.
(a) and (b) of FIG. 14 show an example of a configuration of a liquid crystal display device whose backlight is a conventional direct light type illuminating device using a linear light source such as a cold-cathode tube. A liquid crystal display device 100 shown in FIG. 14 includes a liquid crystal display panel 101 and a backlight 102 for radiating light to the liquid crystal display panel 101. The backlight 102 includes a plurality of cold-cathode tubes (linear light sources) 111, a reflective plate 112, and a diffusing plate 113.
As shown in (a) of FIG. 14, there are provided a plurality of cold-cathode tubes 111, which are aligned along a horizontal direction (lateral direction) d1 in such a manner that the cold-cathode tubes 111 are parallel to each other. The reflective plate 112 is positioned at the back face of the cold-cathode tubes 111 (positioned oppositely to a side of the cold-cathode tubes 111 which side faces the liquid crystal display panel 101), and reflects the light from the cold-cathode tubes 111 so that the light is directed toward the liquid crystal display panel 101. The diffusing plate 113 diffuses the light from the cold-cathode tubes 111 so that the light is directed toward the liquid crystal display panel 101.
(a) of FIG. 14 shows a relationship between a width a of an effective display region of the liquid crystal display panel 101 and a length b in a long side direction of the cold-cathode tube 111. Here, the effective display region of the liquid crystal display panel 101 indicates a region obtained by removing, from a whole region of the liquid crystal display panel 101, a peripheral region (frame region) where drive circuits for driving various lines and other components are provided. The length b in a long side direction of the cold-cathode tube 111 indicates a length in a long side direction from one end of the outer shape of the cold-cathode tube 111 serving as a linear light source to the other end thereof.
As shown in (a) of FIG. 14, in the conventional liquid crystal display device 100, each end of the cold-cathode tube 111 is positioned at the outside of the effective display region. That is, the effective display region is included in an area defined by the length b of the cold-cathode tube 111.
In the example shown in (a) of FIG. 14, an explanation was made as to a configuration in which the cold-cathode tubes 111 are positioned along a lateral direction of the liquid crystal display panel 101. It should be noted that in a configuration in which the cold-cathode tubes 111 are positioned along a longitudinal direction of the liquid crystal display panel 101, a relationship between a width of an effective display region of the liquid crystal display panel 101 and a length in a long side direction of the cold-cathode tube 111 is the same as that in the case of the configuration in which the cold-cathode tubes 111 are positioned along a lateral direction of the liquid crystal display panel 101.